Hydraulic pit props



United States Patent HYDRAULIC PIT PROPS Wilhelm Liibbe, deceased, late of Oberaden, Germany, by Armin Lijbbe, administrator, Oberaden, Germany Application April 6, 1950, Serial No. 154,412 Claims priority, application Germany April 7, 1949 1 Claim. (Cl. 248-354) This invention relates to hydraulic pit props of the kind in which a lower portion acts as a cylinder within which a piston acts as a displaceable upper portion.

The most sensitive and, as regards production, the most expensive part of such a prop is the sliding surface of the displaceable piston, since this surface must fit tightly in the cylinder under very considerable pressure both in continuous working and when the prop remains in position for several days. The piston surface, projecting out of the lower portion when the prop is in position, is very susceptible to damage in rough mining. When the prop is under load, there are produced more or less heavy breaking stresses which can lead to damage of the sealing surfaces between the cylinder and piston.

An object of the invention is to provide a hydraulic prop in which the aforementioned disadvantages are obviated or reduced.

According to the present invention there is provided a hydraulic pit prop including a lower part formed as a cylinder and an upper part formed as a piston. The piston is slidable within the cylinder and comprises a tube which is open at its upper end in which end an inner prop is supported. This inner prop is adapted to support a load, and the length of said inner prop is adjustable.

With this construction, the extensible length needs only to be practically as great as the greatest fluctuation in the seam thickness that is to be expected. However, any shortening of the sealing surface also results in a corresponding reduction of the production costs. Also with this construction only a comparatively short piece of the cylindrical sealing surface of the displaceable piston projects out of the cylinder at any time, so that the danger of mechanical damage during constant use thereof, and particularly during its removal, is essentially less than if a length of piston of about half the seam thickness were to project out of the cylindrical lower portion. The resistance capacity of the sliding surface of the piston to mechanical and also chemical influences may be further increased by the hardening of that surface and, in certain cases, chromium-plating of that surface.

In order to obviate the necessity for supplying special inner props for slight differences in the seam thickness, it is proposed, according to the invention, to support the inner prop within the piston by interposing a support member, the external diameter of which is smaller than the internal diameter of the inner prop and which is provided, at or near its upper end, with a collar engaging under the inner prop. With a relatively small seam thickness, this support member can then be so fitted that the end carrying the collar is turned downwards, so that its longer end engages in the inner prop.

The upper and lower portions of the prop and also the inner prop inserted in said lower portion are rigidly supported one within the other. In order to keep breaking stresses as low as possible, it is advisable that the prop be supported against the floor as well as against the roof by means of a ball joint.

One embodiment of the invention is shown in the accompanying drawing, partly in elevation and partly in vertical section.

The lower portion 10 of the prop is formed as a tubular cylinder which is closed, and is formed into the shape of a hemispherical dish at its bottom end, as shown at 11. This base rests in a foot plate 12 which is also formed into the shape of a dish and which-is provided with a supporting flange 13 welded thereon; The supporting foot 12, and the flange 13 is held by means of clips 14 welded to the lower portion 10 of the cylinder so that the foot and flange always remain loosely connected to the jack, but there is the possibility of turning between the parts 10 and 12.

A tube 15 which is closed at its bottom end at 16 but is open at its upper end at 17 is provided within the cylinder 10 to act as an extensible hydraulic piston. For sealing the two parts 10 and 15 in relation to one another, suitable sealing or packing means are provided at 18. Water under pressure may be introduced into the cylinder 10 via a non-return valve 19, which is opened when the piston 15 is lowered and the prop removed. In addition, a safety valve 20 is provided, by the adjustment of which the maximum supporting capacity of the prop can be regulated.

In order to make the upper area of the extensible prop piston 15 as resistant as possible to mechanical stresses or to chemical influences, it may be hardened and, after grinding, it may also be provided with a coating of chromium.

The use of previously known iron pit props has been limited by their maximum extensibility and when a pit prop has been used with a seam of very small thickness it has sometimes been found that the length of the lower portion of the prop is generally only slightly less than the seam thickness. With a hydraulic prop, that would mean that with the maximum length of the prop, the highly finished surface of the displaceable piston is almost equal to half the seam thickness. It is obvious that, in such a case, the danger of mechanical damage to the piston surface is very great. With the prop illustrated and constructed in accordance with the invention, the displaceable length between the lower portion 10 and upper portion 15 of the prop is substantially less than the thickness of the seam. The extra length required is provided by an inner prop 22 adapted to the thickness of the seam, this inner prop being rigidly engaged in the pot-shaped piston 15. The prop head 23 is also connected with the inner prop 22 by a ball joint. If props according to the invention are to be set up in a seam of greater or lesser thickness, only the inner props 22 need to be adapted to the changed seam thickness. It is to be assumed that the inner prop 22 is directly supported on the base 16 of the pot-shaped piston 15.

A further effective means for adapting the prop length to the seam thickness consists in the use of a support member 24 which in turn is inserted between the base 16 of the piston 15 and the bottom rim 25 of the inner prop 22. This support member 24 may be so constructed that its external diameter is less than the internal diameter of the inner prop 22. In this case, the support member is provided with a collar 26 which is disposed near the upper end of the support member 24. As can be seen from the drawing, the bottom rim of the inner prop 22 is supported in this case on the collar 26 of the support member 24 and this in turn rests on the base 16 of the pot-shaped piston 15. The extensible length of the prop can then be reduced in a simple manner by reversing the position of the support member 24, so that its collar 26 is disposed in the vicinity of the piston base 16. If then the inner prop 22 is inserted, it engages over the largest part of the support member 24 and is finally supported with its bottom rim 25 on the second end face of the collar 26. When setting up the prop in a scam, the necessary extensible length generally only fluctuates in small limits, so that it is only occasionally necessary to change the inner prop 22 or to reverse the support rnember24. The inner prop 22 may be attached by a screw 27 or the like to the piston 15.

I claim: 7

A hydraulic pit prop comprising a lower supporting .member defining ahydraulic cylinder, a hollow tube shaped piston slidably positioned within said cylinder, said piston being open at its upper end', a lower, substantially cylindrical "support member removably positioned and supported within said piston and having a collar located nearer to one end portion of the support member-than the other, and a hollow upper member telescopically positioned about said lower support member resting on said collar, whereby .said lower support member may be reversed or removed to vary the height of the inner prop.

References Cited in the file of this patent UNITED STATES PATENTS 

